Effect of solvent upon competitive liquid-liquid extraction of alkali metal cations by isomeric dibenzo-16-crown-5-oxyacetic acids

The selectivity and efficiency of competitive liquid-liquid extraction of alkali metal cations into organic solvents containingsym-(octyl)dibenzo-16-crown-5-oxyacetic acid (2) andsym-bis[4(5)-tert-butylbenzo]-16-crown-5-oxyacetic acid (3) have been determined. Solvents examined include: dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, 1,1,1-trichloroethane, benzene, toluene,p-xylene, chlorobenzene, 1,2-dichlorobenzene, and 1,2,3,4-tetrahydronaphthalene. The Na⁺/K⁺ and Na⁺/Li⁺ extraction ratios are highest in chloroform. The extraction selectivity is found to correlate with the diluent parameter (DP) of the organic solvent.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

戊烯自由基阳离子的密度泛函理论研究

使用密度泛函理论B3LYP方法和6-31G(d,p)、6-31＋G(d,p)、6-311G(d,p)及6-311＋G(d,p)基组，分别对2-C5H10＋和1-C5H10＋的各种构象进行了几何构型优化，并用B3LYP/6-311G(d,p)进行了频率分析计算.计算预言1-C5H10＋具有非平面构型，与以往报导的从头算计算结论相反.在两个自由基阳离子的各种构象的B3LYP几何构型上，进行了B3LYP和UMP2(full)方法的超精细偶合常数计算，得到了比以往更好的结果.     

Functionalization of montmorillonite by acrylamide polymers containing side-chain ammonium cations

Stable polyacrylamide (polyAA)–montmorillonite adducts were prepared by two distinct processes: (1) free radical copolymerization of AA with alkaline clay previously treated with 2-(N-methyl-N,N-diethyl ammonium iodide)ethylacrylate (QD1) and (2) direct interactions of alkaline montmorillonite with various preformed copolymers of AA with QD1. The structure of the adducts as determined by Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry and X-ray diffraction was shown to consist of AA macromolecules inserted between lamellar layers whose spacing was larger than in the polymer-free clay. The polymer was strongly attached to the inorganic surfaces, probably due to cooperative formation of electrostatic bonding. The thermal stability of the organic polymers in the resulting complexes was substantially enhanced while the mobility of macromolecules decreased.     

High-performance liquid chromatography using a color-forming agent as a mobile phase component. Separation of alkaline-earth-metal cations with arsenazo III and a non-porous gel column

Summary A liquid chromatographic procedure for separating alkaline-earth-metal cations with a non-porous gel column has been developed. Arsenazo III, which is one of the sensitive and commercially available color-forming agents, was used as a component of the mobile phase. Magnesium and calcium could be separated on the nonporous gel column within 55 seconds. The procedure was suitable for the separation of alkaline-earth-metal cations in relatively pure solutions with high sensitivity. Because of its rapidity the described procedure is also potentially applicable for any aqueous sample.     

Molecular complexes of crown ethers. Part 3. Effect of cations on charge transfer complexes with TCNE

The intermolecular charge transfer complexes (CT) of two crown ethers (CE), viz, B15C5 and DB18C6 (as donors), and tetracyanoethylene (TCNE), as acceptor, were studied in the UV-visible region in dichloroethane (DCE), at 298.2 K. The sequence of addition of the cation was varied in the case of B15C5 such that in one system the sequence was (CE+Cation)+TCNE and in the other (CE+TCNE)+cation. These two systems were found to be non-interchangeable, even under reflux conditions, giving differentK _c values which were explained as being due to the different geometries of the CE. For the first sequence, the values most affected depended on the fit of the metal cation with the ether cavity, thus in B15C5, Na⁺ showed the greatest effect, while for DB18C6 it was K⁺.     

Retention of ionizable compounds on high-performance liquid chromatography. VII. Characterization of the retention of ionic solutes in a C18 column by mass spectrometry with electrospray ionization

The elution of ions from a C₁₈ column with mobile phases containing methanol (60%, v/v) and aqueous buffers is studied by mass spectrometry. It is demonstrated that the anions are excluded from the stationary phase by the ionized silanols. However, the ionized silanols interact strongly with cations, which are retained in the column. These cations are later eluted from the column by ion exchange with the cations present in the pH buffered mobile phase. The size of the ions, the mobile phase cation concentration and the mobile phase pH are the main parameters that affect elution of the retained cations. It is also demonstrated that there are at least two different types of ionizable silanols, with different acidities, that contribute to the retention of cations. An estimate of the pK_a values of these two groups of silanols in 60% methanol is given.     

From Weakly Coordinating to Non‐Coordinating Anions? A Simple Preparation of the Silver Salt of the Least Coordinating Anion and Its Application To Determine the Ground State Structure of the Ag(η2‐P4)2+ Cation

The unexpected but facile preparation of the silver salt of the least coordinating [(RO)₃Al‐F‐Al(OR)₃]^? anion (R=C(CF₃)₃) by reaction of Ag[Al(OR)₄] with one equivalent of PCl₃ is described. The mechanism of the formation of Ag[(RO)₃Al‐F‐Al(OR)₃] is explained based on the available experimental data as well as on quantum chemical calculations with the inclusion of entropy and COSMO solvation enthalpies. The crystal structures of (RO)₃Al←OC₄H₈, Cs⁺[(RO)₂(Me)Al‐F‐Al(Me)(OR)₂]^?, Ag(CH₂Cl₂)₃⁺[(RO)₃Al‐F‐Al(OR)₃]^? and Ag(η²‐P₄)₂⁺[(RO)₃Al‐F‐Al(OR)₃]^? are described. From the collected data it will be shown that the [(RO)₃Al‐F‐Al(OR)₃]^? anion is the least coordinating anion currently known. With respect to the fluoride ion affinity of two parent Lewis acids Al(OR)₃ of 685 kJ mol^?1, the ligand affinity (441 kJ mol^?1), the proton and copper decomposition reactions (?983 and ?297 kJ mol^?1) as well as HOMO level and HOMO–LUMO gap and in comparison with [Sb₄F₂₁]^?, [Sb(OTeF₅)₆]^?, [Al(OR)₄]^? as well as [B(R^F)₄]^? (R^F=CF₃ or C₆F₅) the [(RO)₃Al‐F‐Al(OR)₃]^? anion is among the best weakly coordinating anions (WCAs) according to each value. In contrast to most of the other cited anions, the [(RO)₃Al‐F‐Al(OR)₃] anion is available by a simple preparation in conventional inorganic laboratories. The least coordinating character of this anion was employed to clarify the question of the ground state geometry of the Ag(η²‐P₄)₂⁺ cation (D_2h, D₂ or D_2d?). In agreement with computational data and NMR spectra it could be shown that the rotation along the Ag‐(P‐P‐centroid) vector has no barrier and that the structure adopted in the solid state depends on packing effects which lead to an almost D_2h symmetric Ag(η²‐P₄)₂⁺ cation (0 to 10.6° torsion) for the more symmetrical [Al(OR)₄]^? anion, but to a D₂ symmetric Ag(η²‐P₄)₂⁺ cation with a 44° twist angle of the two AgP₂ planes for the less symmetrical [(RO)₃Al‐F‐Al(OR)₃]^? anion. This implies that silver back bonding, suggested by quantum chemical population analyses to be of importance, is only weak.     

Kinetics and Substrate Selectivity of the Oxidation of Saturated Hydrocarbons by Adamantyl Cations in Sulfuric Acid

It was shown that at 70 °C sulfuric acid ([H₂SO₄] > 85 wt.%) solutions of 1-hydroxyadamantane and the solutions obtained in the reaction of adamantane with concentrated sulfuric acid oxidize saturated hydrocarbons (RH). Data on the kinetics, selectivity, kinetic isotope effect, and the effect of the acidity of the medium on the oxidation rate of RH indicate cleavage of the C—H bond in the substrate at the rate-determining stage and the direct participation of adamantyl carbocations.     

Kinetics of proton exchange between semiquinone radicals and hydrochloric acid

The mechanism of proton exchange between semiquinone neutral radicals 3,6-di-tert-butyl-2-hydroxyphenoxyl (1), 6-tert-butyl-3-chloro-2-hydroxy-4-triphenylmethylphenoxyl, and hydrochloric acid in toluene solutions has been studied. The rate of proton exchange with hydrochloric acid is less than that with acetic acid owing to the higher thermodynamic stability of the radical cation formed upon semiquinone radical protonation by hydrochloric acid. The formation of radical cations and their dimers has been proven by spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No 1, pp. 84–87, January, 1993.     

Use of 1-alkyl-3-methylimidazolium hexafluorophosphate room temperature ionic liquids as chelate extraction solvent with 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione

Possible use of room temperature ionic liquids (RTILs) as chelate extraction solvent was evaluated by using 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF₆]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([omim][PF₆]). These RTILs showed high extraction performance for divalent metal cations with 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (Htta). The extracted metals were back-extracted into 1 mol dm⁻³ nitric acid quantitatively. Furthermore, the extracted species were estimated as neutral hydrated complexes M(tta)₂(H₂O)_n (n= 1 or 2) for M = Ni, Cu and Pb and anionic complexes M(tta)₃⁻ for M = Mn, Co, Zn and Cd.